A shear constitutive model and experimental demonstration considering dual void portion and solid skeleton portion of rock

Shear deformation and break is a typical failure phenomenon of engineering rock. Building a constitutive model for rock shearing behaviors is a key issue in stability assessment of geotech-nical engineering. A dual-structure shear constitutive model was developed to reveal the full shearing deformation evolution features of geological material. It was assumed that the rock was composed of void portion and solid skeleton portion. Thus, the macro constitutive relation of rock shearing deformation was established by accumulating the micro voids' shear deformation and solid skeleton deformation. The comparison analysis of four geological materials indicated that the constitutive model can fully characterize the shear deformation and failure evolution process of rock, including the compaction stage, linear elasticity, shear hardening, shear softening, bimodal phenomenon and residual stages. At the micro level, the damage variable (D) evolution of solid skeleton can be divided into three stages: (i) pre-damage stage; (ii) accelerated damage deterioration stage; and (iii) completed damage stage. It was worth paying attention to the Weibull parameters (m, u0), where parameter m reflected the brittle failure characteristics of the rock, and parameter u0 indicated shear peak strain and peak strength of rock. Finally, physical shear experiments for cemented paste backfill-rock were carried out and the bimodal shear failure mechanism was comprehensively analyzed based on the proposed constitutive model.

Automated summary

Shear deformation and failure are common in engineering rock, and developing a constitutive model to understand these behaviors is crucial for stability assessment in geotechnical engineering. A dual-structure shear constitutive model was designed, considering both the void portion and solid skeleton portion of the rock. This model successfully characterized the complete evolution of shearing deformation in four geological materials, including compaction, elasticity, hardening, softening, bimodal phenomenon, and residual stages. The micro-level analysis revealed three stages of damage deterioration in the solid skeleton, and the importance of Weibull parameters (m, u0) in indicating the brittle failure characteristics and peak strain/strength of the rock. Furthermore, physical shear experiments were conducted on cemented paste backfill-rock, and the bimodal shear failure mechanism was comprehensively analyzed using the proposed constitutive model.